Digital three-dimensional manufacturing, also known as digital additive manufacturing, is a process of making a three-dimensional solid object of virtually any shape from a digital model. Three-dimensional printing is an additive process in which one or more ejector heads eject successive layers of material on a substrate in different shapes. Typically, ejector heads, which are similar to printheads in document printers, include an array of ejectors that are coupled to a supply of material. Ejectors within a single ejector head can be coupled to different sources of material or each ejector head can be coupled to different sources of material to enable all of the ejectors in an ejector head to eject drops of the same material. Materials that become part of the object being produced are called build materials, while materials that are used to provide structural support for object formation, but are later removed from the object are known as support materials. Three-dimensional printing is distinguishable from traditional object-forming techniques, which mostly rely on the removal of material from a work piece by a subtractive process, such as cutting or drilling.
A previously known three-dimensional object printing system 10 is shown in FIG. 8. In the view depicted in that figure, the cart 14 (FIG. 8) moves in a process direction P on precision rails 38 underneath the printing station 26. Precision rails 38 are cylindrical rail sections that are manufactured within tight tolerances to help ensure accurate placement and maneuvering of the cart 14 beneath the ejector heads 30. Linear electrical motors are provided within housing 42 to interact with a magnet inside housing 46 (FIG. 7) connected to the lower surface of the cart 14, as described below, to propel the cart 14 along the track rails 22 between printing stations 26. Once the cart 14 reaches the rails 38, the bearings 34 transition to the precision rails 38. As the cart 14 passes beneath the printing station 26, the ejection of material occurs. Electrical motors (not shown) are configured to move the ejector heads 30 in an X-Y plane that is parallel to the process direction P as layers of material are printed on the cart 14. Additional motors (not shown) move the printing station 26 vertically with respect to the cart 14 as layers of material accumulate to form an object. Alternatively, a mechanism can be provided to move an upper surface of the cart 14 on which the object is being formed vertically and horizontally with respect to rails 38 as the layers of the object are formed. Once the printing to be performed by a printing station is finished, the cart 14 moves to a position that enables the bearings 34 to contact rails 22 so the cart can slide along the rails 22 to another printing station for further part formation, layer curing or other processing.
An end view of the prior art system 10 is shown in FIG. 7. That view depicts in more detail the relationship between the cart 14 and the track rails 22 as well as the precision rails 38. In the area underneath a printing station 26, bearings 34 of the cart 14 are positioned on the precision rails 38 in an arrangement that facilitates accurate positioning of the build platen on the cart 14. Specifically, bearings 34 are positioned at a right angle to one another on one of the rails 38 to remove 4 degrees of freedom of the cart 14, while the other bearing 34 is perpendicular to the other rail 38 to remove one more degree of freedom. Linear motors within the housing 42 generate electromagnetic fields that interact with the magnet in housing 46, which has a bottom surface 50, to move the cart 14 along the precision rails. Gravity and magnetic attraction between the stationary motor segment and the magnet within housing 46 hold the bearings 34 in contact with the rails 38. Extensions from the rails 22 fit in the slots 52 of the cart 14 to enable the cart to slide along the extensions between printing stations 26 as the linear motors propel the cart.
When a cart is not present underneath the ejector heads 30, errant drips of materials can fall from the ejector heads and produce undesired debris and contamination on an area 54 that can include the precision rails 34, the track rails 22, and the housing 42. In order to produce three-dimensional objects with acceptable quality, the motion of the cart 14 beneath the ejector heads 30 needs to be precise. If materials from the ejector heads collect where the bearings 34 interface with the precision rails, the linear velocity of the cart is disrupted and the quality of the printed object is affected. Additionally, the collection of material drops on top of the housing 42 may affect the dissipation of heat from the motors and impact the performance and reliability of the motors. Therefore, improvements in three-dimensional printing systems that help eliminate the contamination on the precision rails and motor housing that affects the accuracy of the placement and movement of the cart would be beneficial.
Devices have been produced that enable clearing of undesirable material from tracks. Metal flaps and plows positioned in front of wheels on a railroad engine have been used to clear materials such as ice and snow from railroad tracks. Wiping cloths or cleaning tissues affixed to an underside of model trains have also been used to wipe undesired materials from model railroad tracks. However, such techniques are not optimized for use in removing materials used in three-dimensional printing, which may solidify or cure after being ejected. Such techniques are also not adapted to cleaning curved surfaces. Hand-tools having a curved edge adapted to scrape a curved surface have been produced, but such hand-tools are not optimized for cleaning materials used in three-dimensional printing or for cleaning along a continuous track.